text:
How does a flux gate compass system work?
I have heard of gyroscopes and AHRS being used for heading indication, but I haven't heard of a flux gate compass system until recently.
What are the principles of its operation and what types of aircraft or systems are currently using it?

Fluxgates are a way to determine a magnetic field, in this case for navigational purposes. The basic principal is based on the lines of flux that the magnetic field of the planet gives off, a nice overview can be found here:

The flux gate compass that drives slaved gyros uses the characteristic
  of current induction. The flux valve is a small, segmented ring, made
  of soft iron that readily accepts lines of magnetic flux. An
  electrical coil is wound around each of the three legs to accept the
  current induced in this ring by the Earth’s magnetic field. A coil
  wound around the iron spacer in the center of the frame has 400 Hz
  alternating current (AC) flowing through it. During the times when
  this current reaches its peak, twice during each cycle, there is so
  much magnetism produced by this coil that the frame cannot accept the
  lines of flux from the Earth’s field.

There is a good video here as well.
Older, pre-glass HSI's are often slaved directly to them, like this one. On newer systems the flux-gate is a component of the AHARS.
Lots of aircraft use them, they can be installed on everything from a small GA plane all the up though an A380. These days they are fairly small units.

Is an instrument like the Garmin GMU 11 based on a flux gate?  https://buy.garmin.com/en-US/US/p/574236/pn/010-01788-00  "GMU 11 is an affordable, microprocessor-based magnetometer. It can be used to accurately sense the Earth’s magnetic field alignment and provide this data to compatible ADAHRS processors for use in referencing aircraft magnetic heading. In essence, the magnetometer acts as an electronic compass, showing the ADAHRS which direction the aircraft is facing in relation to magnetic north."

And "Unlike conventional flux valve systems, which detect only the horizontal component of the Earth’s magnetic field, the GMU 11 magnetometer provides full 3-axis vector measurements for the most precise digital indication of magnetic field strength and direction."

@CrossRoads no but the GUM 44 is

I'm not seeing GUM 44 as a flux gate at Garmin or in Google.

Altho I did get plenty of entertaining hits with GUM 44 flux capacitor :)

@CrossRoads sorry the GMU44 (its in the linked doc)

I don't think it is. Section 2.5.2 says: The GMU 44 is an extremely sensitive three-axis magnetic sensor. It is more sensitive to nearby magnetic disturbances than a flux gate magnetometer.


text:
What is the difference between an Non-Directional Beacon and a Compass Locator Beacon?
What is the difference between a Non-Directional Beacon and a Compass Locator Beacon?

Normally "Compass Locator Beacons" were co-located with the outer marker for ILS approaches. A "compass locator beacon" is an NDB beacon specifically to drive the radio compass.
A radio compass was a lot simpler instrument than the ADF that worked off of the NDB beacons. Typically it just had a needle that pointed left/right to direct the pilot to turn towards the station. They operate on the same frequencies as ADF/NDB and can be tuned with an ADF receiver.
Radio compasses used the old "loop antennas" that you see on old aircraft pictures. The pilot, co-pilot, or navigator would rotate the antenna by hand (the older radio navigation system required the pilot to turn, so rotating antennas were a step up) to be able to find the bearing to a particular station.
ADF (the "automatic" part of the "automatic direction finder) eliminated the need to rotate the antenna to get the direction to the NDB.
So to answer the question, the NDB and the compass locator beacon are technologically the same, it is the equipment in the aircraft that changed.
See NDB Nav History for more details

Ah okay, so a compass locator is kind of like one of those handheld antennas that they (used to?) use to locate ELT signals.  It didn't point, it just tippled left, right, or would center if you faced the right direction.  Is that how that "Compass locator" instrument works?  I have never seen one before.

That's pretty much right. There is a picture of one in the link at the bottom of my answer if you're curious what they look like.

As far as differences go, Locators generally use lower power for the transmission. Also, by way of info, it was not uncommon to have another locator coincident with the ILS 'middle marker' which was typically around the 200ft ILS Cat1 minimums thus indicating passage past the Decision Altitude.

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text:
What is this pattern on this runway?
What is this pattern on this runway? What is its function?

Location on Google Maps

To be honest, this device shown here is aviation-related (They use it to check the RCS of aircraft/aircraft parts), it is just not a runway.

It is not a runway that you see there. It is the US Navy's Radar Cross Section Range at Junction Ranch. From what I know, that is the platform on which they put the object which they want to see the Radar Cross Section of on. There is a radar at the other end of the "runway".
This is what it looks like:

Image Source

NB: They do the same with ships. They circle in front of a coastal installation.

Interesting answer, but it doesn't seem to answer the question of What is this pattern. No downvote here, just saying.

Looking at the pattern, it appears to be markings on the surface of a turntable and the surrounding structure. The turntable is rotated maybe 55° clockwise from the surrounding structure. The three red lines are probably used to center the landing gear and orient the aircraft on the turntable.

@JonathanWalters The second sentence in the answer says, "It is the platform..." which does say what it is.

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text:
What's this tiny airplane?
I found this very small airplane in the desert on Google Maps. It appears to have about
a 10 foot wingspan, and is about the size of an SUV (compare to cars nearby).

Location in Google Maps: Google Maps

Since its near the Naval Air Weapons facility in China Lake, I'd guess that it is a target drone.

I would make this a comment since I can't be certain, but I wanted to put some photos in. I concur with Ron that it's a target drone. But what target drone?
The one next to it appears to be a Ryan BQM-34 Firebee.
The most likely possibility is the Beachcraft MQM-107 Streaker.
Here is a chart of US target drones.

source

The Lahshya doesn't look right. Maybe a MQM-107B Streaker or similar variant? Doesn't seem exactly right, but seems close.

I'd expect to see at least a hint of a shadow on the inboard section of the right wing if it was a low wing.  Also, the horizintal seem wider than on the orange drone. Maybe just me, but the nose looks to have a "spike" on the nose (similar to a MiG21). My knee jerk reaction is some kind of old cruise missile that was never test fired. Not sure that makes much sense though. Why leave it out in the open...unless to be photographed by the soviets.

Now I am thinking it looks like a variant of a BQM-74. Length is in the right range, at 15 ft, high wing. Wing shape doesn't match any -74 variants I can find, though.

It looks like a display of different drone aircraft. The BQM-34, the A6's to the left, Not sure if that's a P-51, but I think they made target drones out of them too.

@ymb1 I've convinced myself it has to be one of the MQM-107 variants. Not sure which one, but the A variant is likely. I think that larger aircraft there is an F-8 which were also made into target drones

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text:
"The pilot must know the center of gravity and gross weight to fly" -- True or false?
I've been trained to know the calculated gross weight and center of gravity for takeoff and landing for every flight for which I have acted as pilot in command.
I've had other instructors dispute that this is not a requirement and simply being familiar enough with the aircraft to reasonably be able to estimate that you're within C.G. tolerances considering the fuel and passengers is satisfactory.
Are there any regulations that explicitly define the requirements of pre-flight weight and balance familiarization for civil airplanes requiring an AFM containing takeoff and landing distance data?
If not, surely there is some catch-all so lawyers can sue us easier; what would that most likely be based on case law? 14 CFR 91.13, the "all available information concerning that flight" clause from 14 CFR 91.103, or something else?
Note that 14 CFR 91.103(b) requires familiarization with runway lengths of intended use and takeoff and landing distance data for any flight; myself and others would argue that being able to meet that condition would require, at a minimum, familiarization with certain weather metrics and knowing the airplane's loaded gross weight.
However, I am still not seeing an explicit requirement to know a specific C.G. figure.

I don't have enough detailed knowledge of the legal requirements, but wouldn't knowing the CG be a necessary step to ensure the aircraft is loaded within its safe envelope? Mostly because "being familiar enough with the aircraft to reasonably be able to estimate that you're within C.G." is the equivalent of "it felt right to me, no idea why it stalled on takeoff, Your Honor" and won't stand up to scrutiny. We stopped flying like that in the 60-70s, thankfully

I'd expect any requirement to be about the gross weight/CG envelope rather than the actual position of the CG,  the sort of thing shown in the graphic here: http://trumpetb.net/alph/wbPA28-140.html
I know of one recent prosecution in the UK for 'endangering an aircraft' that was due to overloading:
https://www.manchestereveningnews.co.uk/news/greater-manchester-news/pilot-jailed-crash-landing-risking-15981019
God knows where that aircraft would be on the graphic when it was overloaded by more than 400lb!

For every flight?  That means that every time I want to take the Cherokee up for a spin, I should do a new weight & balance computation?  I don't think so :-)

@jamesqf Yes, every flight. Of course, if the load will be (roughly) the same as a previous flight and you didn't date your work...

Related

In my training Tomahawk, we couldn’t fill her up with dual crew due MTOM limit, so we took something like 3/4 tanks. I am rather tall, so my seat was far back, and my instructor was shorter, so a bit more forward. CG and mass was calculated once, aircraft basic index wasn’t modified ever, and all flights used same setup. I can assure you that CG calculation was meticulously done and cross checked once prior first dual flight and then once prior first solo (full tanks now). Any time after that, we’d brief that we were in known standard configuration.

Don't get me wrong, if the loading conditions are identical, then by all means don't waste trees for subsequent flights.

The exception of course is a proper flight plan, where only using precise numbers will ensure precise fuel calculations. On a training sortie, simply calling it “standard numbers” was absolutely acceptable.

@jamesqf Do it on an app. Will take you 30 seconds on a Cherokee. Heck, it takes maybe 2 minutes to do that on a full-size jet these days, and most of that's double-checking the numbers.

@user71659: It's not whether it would take 30 seconds or 30 minutes, it's that it's pointless.  My weight does not change by a significant amount between flights (indeed, it hasn't changed much in my adult life); I know the Cherokee can carry 4 people and fuel, so with just me I'm well within limits.  I'd expect the same to be true if I borrowed a 172 or similar plane.  I would do a calculation only if I was going to carry a load that concievably might exceed weight & CG limits.

True. It is the pilot-in-command's responsibility to determine if the aircraft is safe for flight. 14 CFR § 91.3(a) makes the PIC directly responsible for that.
The 2016 FAA Weight and Balance Handbook also states:
4. The pilot in command (PIC) has the responsibility
prior to every flight to know the maximum allowable
weight of the aircraft and its CG limits. This allows
the pilot to determine during the preflight inspection
that the aircraft is loaded so that the CG is within the
allowable limits

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text:
What is the maximum distance for class C service?
Sectionals say to contact the approach center of a class C airspace within 20 miles. Is this a suggestion or a rule?
What is the maximum distance to contact them via radio, other than signal limitations, if one exists?
What is the maximum distance to receive radar service from class C?
Note that class C radar service and flight following from an ATC center are not the same thing as it pertains to my question.

There is no strictly defined "maximum distance" beyond which you cannot receive radar service from an approach-control-whose-primary-airport-is-a-Class-C.
Terminal areas around a Class C airport generally comprise a 5-mile inner ring, 10-mile outer ring, and 20-mile outer area.  The Approach Control is guaranteed to own the airspace laterally bounded by the outer ring of the Class C, extending upwards to their delegated ceiling (usually 10-to-12 thousand feet MSL) whether Class C or Class E; they are all but guaranteed to control the Class E airspace with 20 miles as well.1  Within that usually-20-miles and usually-10-kft cylinder of airspace, they will provide Class C services to all participating aircraft, even if the aircraft happen to be in Class E airspace—which is obviously more statistically likely, given the relative airspace volumes!  However in Class E airspace you're not required to talk to them, whereas in Class C you are.
The reason the box says "CTC KNOXVILLE APP WITHIN 20NM" is that 20 miles guarantees you're within the "outer area" and thus Approach's airspace.  If you contacted them at 30 miles out, you may be Center's airspace, in which case Approach would need to redirect you to Center, and then Center would hand you back to Approach a few minutes later.  That's a waste of both your time and the controllers' time, so the chart reminds you of the minimum range to help you avoid that.
There is no theoretical maximum, and many Approach facilities do in fact control more (sometimes far more) airspace than the minimum.  In this beyond-20-mile area you will not receive Class C services, but the airspace still belongs to the Approach rather than to the Center. However, the FAA does not publish the actual sector boundaries, so the best practice is to assume no more than the minimums—or get Flight Following for your entire trip, in which case you don't have to worry about it at all.

1The "procedural outer area" is, by default and in most cases, defined by a 20-mile ring around the primary airport.  But in congested or mountainous areas—e.g. OAK, MDW, or SBA—this may not always hold true...

20 miles from the airport or outer airspace ring?

@RyanMortensen All distances are from the primary airport.  If you draw a circle at 20 miles, it (usually) passes through the "CTC APP" boxes, which is a subtle clue.

That makes sense, but I never knew that. Thanks!

@Ryan 25-30 miles out shouldn't usually be a problem, and IMO sooner is better. If necessary the controller can get a pointout from the controller who owns the airspace you're in, but if you're near to the boundary and they don't need to issue any immediate control instructions it isn't a big deal to let you run for a few miles. Neighboring controllers will recognize the squawk bank and know you're inbound to XYZ approach's airspace.

Coming back to this answer, I really must take exception to several of your points, especially There is no such thing as "Class C radar service". I think I understand what you are trying to say, but as @Ryan said in his question, "Class C service" is a very well-defined concept and is not the same as basic VFR radar service—namely, when providing Class C service ATC will ensure positive separation between IFR-VFR traffic, while basic radar service only provides traffic advisories and safety alerts between IFR-VFR traffic.

I ended up editing your answer rather heavily; if you feel the changes go beyond helpful clarifications, feel free to roll back the edit and I will post my own answer.

@randomhead You’d know the details better than I.  As a pilot, though, can I even tell (without looking at a chart) which service I’m receiving? If not, how meaningful is the distinction? It’s not like you’re going to let planes crash into each other just because they’re 21 miles away.

Even with a chart you wouldn't know for certain—the procedural outer area is not charted (although you would know that at the very least it extends upward above the charted Class C until reaching the ceiling of Approach's airspace). And your point is well-taken that a controller would certainly act to prevent a collision. But the fact remains that in (most) Class E airspace there is no defined minimum between an IFR aircraft and a VFR aircraft, while in Class C airspace (and its associated Class E outer area) there are defined minima.

Is this a suggestion or a rule?

Rule, if you are VFR and landing there.
If IFR, or VFR with flight following, you will be told when to contact approach when arriving from elsewhere, and approach will hand you off to tower. If just passing by, I would at least monitor them to help with situational awareness of traffic in the area.

What is the maximum distance to contact them via radio, other than signal limitations, if one exists?

I'd be contacting them within at least 10 miles, before you enter the Class C airspace.
You can try them as far out as you can receive the ATIS.  For example, I was flying VFR into Binghamton, NY (BGM) and called them out about 20 miles after picking up the ATIS - and they told to enter right base for the active runway and I was cleared to land!  Slow day I guess, not much other traffic.

What is the maximum distance to receive radar service from class C?

Usually 10 miles. If VFR and departing the area, they'll often ask you to advise them when you are leaving the Class C. If flight following was requested, they can hand you off to approach quite soon, like 500 to 1000 ft AGL.


text:
What is the largest flight school in the U.S. that does not offer a degree?
Definition of "largest" for the purpose of this question: the greatest number of flight operations per year on average.
What is the largest flight school in the United States that does not offer a degree?

Is this essentially "what is the biggest part 141 flight school" or what are you looking for?

Probably the US Air Force, unless you're excluding that.

I would like to confirm that I am excluding all military academies.  The scope is for-profit institutions that are open to the general public.

@RonBeyer I am not concerned about part 141 vs. 61.  Public colleges that offer 4-year degrees can operate as either.  If you want to know my personal motivation for asking the question, it is because I am not interested in a program that requires college enrollment to participate in a flight training program, but I also want something that has volume and regular experience providing successful training.

According to Wikipedia, "ATP Flight School ... is the largest flight training company in the United States."
However, volume does not necessarily mean quality, and the focus of ATP and other big-name flight schools seems to be on students who want an airline career—and pushing them through the training as quickly (and profitably) as they can. If that doesn't meet your goals, or you don't have large amounts of both time and money available to dedicate to it, you are probably better served going another route.

Good answer.  I will just add that while ATP may be the largest nationwide COMPANY, their actual footprint at my local airport is quite small compared to two other flight schools at the same field.  (they have just 1 or 2 planes vs more than a dozen)  There are plenty of high quality single site flight schools around the country to choose from, I wish the OP the best of luck finding a good fit.

@MichaelHall I think ATP has 3 or 4 planes at mine, making them the smallest school on the field&,mdash;yet by far the most expensive. I'm sure they're great if you can afford $50k+ to go from zero to ATPL in a month, but that isn't the norm.

@StephenS when I saw this answer last night I realized I did not take into consideration franchise operations.  I had not considered it, but I was actually thinking of the largest single brick and mortar operation.  I wouldn't go to ATP because all of their advertising screams "give me all of your money", and they advertise heavily for people with 0 experience rather than added rating or recurrent training.  I just don't want to be stuck with the weekend warrior who has never had a student who has passed a checkride before or someone who was hired as a reward for spending $50K.

If that's your concern, I would suggest the large schools are the ones you want to stay away from. You want a CFI that does it because they enjoy teaching, not to build (or bill) hours, and those tend to go independent or run small flying clubs.  Word of mouth is the best way to find a good one near you, or at least who to avoid, as unhelpful an answer as that may be.

I don't want to start an extended discussion, and I understand what you mean, but I have mixed feelings on that.  I'll put it this way: the next CFI I hire will go through a job interview.  The smallest and the largest, I would avoid.  A happy medium may be best.  There's an island in the Chesapeake bay where they speak middle-english.  That happens when people are isolated into small groups.


text:
What are ATC-side procedures to handle a jammed frequency?
A few days ago, I was flying into my base airport in the USA with a control tower, and something/someone was jamming the frequency with what the tower thought was a hot mic after I had established communications and received instructions.
They thought it was us with a hot mic (Spoiler: It wasn't), and they managed to somehow broadcast through the hot mic tying up the frequency.
Luckily, that tower operates on two frequencies, so I changed over to the other one and managed to get back in contact with the tower and continued in to the airport; I made sure they knew that we were not the cause of the frequency jam.  That was clear, since nothing was jammed when we changed to the other frequency, plus the original frequency continued to remain jammed.

When such a situation as I describe above happens, what are the procedures that ATC controllers have to follow, and how did they manage to transmit through the hot mic like they did?

Honestly, there is no guarenteed way we can solve such a problem, and it is extremely frustrating when it happens. A few possible solutions:
The radio transmitter associated with the tower frequency is usually quite powerful, so (at least for nearby aircraft) it may be possible to override the other transmission by simply transmitting normally. AFAIK, the transmitter is actually designed to be more powerful than aircraft transmitters as a safety feature. Sounds like this is what happened in your situation. This is usually only the case for tower frequencies (not ground/approach etc.)
Sometimes there is an obvious alternative frequency you can use, and maybe some of the pilots will try tuning to that frequency. We could also do a call on 121.5 and ask everyone tuned to the tower frequency to check for stuck mic. This wouldn't help for small GA aircraft with only one radio, since they won't be listening to 121.5.
In CPDLC airspace (en-route environment), ATC can send a "CHECK STUCK MIC" message to relevant aircraft.
In the end, the pilot with a stuck mic will usually realise after a while of apparent silence on the frequency.
Here is a recording of a stuck mic causing issues at JFK:

For some aircraft they handle a stuck mic in the audio panel. My audio panel in my 177 has a "stuck mic detection" that automatically stops transmitting if the mic is on for more than something like 30 seconds.

@RonBeyer thanks for sharing that.  I had never heard of that before.

@RonBeyer that means if you have a long message to transmit (e.g. description of a medical emergency), you have to split your message into smaller pieces to avoid being cut in the middle of your message, doesn't it?

@ManuH 30 seconds is a long time, I doubt such a limit would cause issues except in very extreme cases

@ManuH Yes, of course, however as J. Hougaard says, 30 seconds is a lot of talking, usually a pilot would just "request medical" either on the runway or at the gate in that case.


text:
What is a metering frequency and why would an airport have it?
I just read a post from a pilot complaining about how he thought a metering frequency was useless.  It has something to do with being on the ground at an airport.
What is it, what purpose does it serve, and what causes an airport to adopt one?

Use of a metering controller and frequency at an airport is one strategy used to prevent congestion on ramps and taxiways. When ready for push back from the gate, pilots call metering. The metering controller will typically either give them permission to push with a ground frequency to call when ready for taxi, or they will tell them to monitor a particular ground frequency for permission to push. They may even tell the pilots to stay on the gate and call back after a specified delay. The use of metering allows the airport controllers to manage ramp and taxi space by sequencing aircraft push and taxi.
Metering control can also help manage potential congestion due to ground delays for situations such as poor weather, runway closures, deicing, flow times into particular destination airports or any other situation that increases taxi time or slows down departures.
Some airports uses different strategies such as discrete ramp areas and frequencies to coordinate push back and taxi flow or internal coordination between controllers.

In order to see metering in action, use http://liveatc.net and monitor the metering freq during bad weather like falling snow, typically at a northern airport like KMSP. Departure ATIS ( not arrival ATIS) will direct all flights to use the metering freq and then the metering freq asks if the flight needs deice. If it does, then metering directs the flight to a deice pad, if it doesn't, it approves it for push back and then tells it to call ground control for taxi.

Have you ever driven into a freeway on-ramp and ran into a traffic light that tells drivers when they can proceed? It's usually turned on during rush hour to prevent jams and accidents. Same thing. It's a flow control method. That pilot was probably unhappy at how long he/she had to wait to be handed over to Ground Control so they could pushback/taxi after contacting the controller on the metering frequency.

"Have you ever driven into a freeway on-ramp and ran into a traffic light that tells drivers when they can proceed?" No, I haven't. Could you explain in a bit more detail what exactly the metering frequency is actually used for?

If you are in the air... A fix along an established route from over which aircraft will be metered prior to entering terminal airspace. Normally, this fix should be established at a distance from the airport which will facilitate a profile descent 10,000 feet above airport elevation [AAE] or above. On the ground, metering is a process by which you call a controller on a freq NOT ground control, and that controller puts you in a queue to contact ground control when they are ready for you. It's flow control. :)

Would be nice if you could add that last description to your answer

@J.Hougaard You're welcome to edit the answer. :)

@J.Hougaard With respect to roadways, see Ramp meter. They're not common in the US and quite rare in the rest of the world.

@MichaelHampton In some states, such as California, they are very common.


text:
What is the danger in the over-use of reverse thrust during ground operations when operating a turboprop powerplant?
I'm new to turboprops, and everyone I've flown with seems extremely cautious about using only the bare minimum reverse thrust after touchdown and never during forward taxi.
Why might that be?

One concern is Foreign Object Damage (FOD). More reverse thrust means more dirt is thrown into the air, which can then be ingested by the engine:

Damage to turboprop engines is not
as common as in jet engines,
because the inlets are generally smaller
and the propeller serves as a first
line of defense. Nevertheless, first-stage
impeller nicks and scratches
are caused when small stones and
debris are picked up from the runway
during propeller reverse pitch
operation after landing.

(Aviation Mechanics Bulletin - Foreign Object Damage)
This is especially true when moving more slowly:

[...] sand and dirt can be ingested causing premature wear and possibly minor damage especially when using reverse thrust at lower airspeeds.

(kingairnation.com, emphasis mine)

We used lots of reverse thrust in the C-130; it was normal to go to full reverse on landing, and also to use some reverse thrust in order to back the plane into or out of parking spots.
The two common cautions were oil temperature (on older engines) and dust ingestion / brown-out (on dirt or unimproved runways).
On early model engines, sustained reverse thrust while taxiing could limit the airflow to the oil coolers, leading to rising oil temperatures. This was avoided by using reverse briefly during taxi - much like avoiding "riding the brakes". Later engines (early 80's aircraft on, iirc) had Oil Cooler Augmentation which solved this.  This used jets of bleed air to pull the necessary volume of air through the oil coolers on the ground, essentially allowing any amount of reverse thrust without concern for oil temperature.
On dirt strips, going to full or nearly full reverse for more than a couple seconds could draw enough dirt up that it would get into the engine inlet, and a few more seconds beyond that you could brown-out your view out the windows.  Coming out of reverse solved the latter, and for the former, it was common to close the engine bleeds during dirt LZ (landing zone) operations, so that the air conditioning system didn't get contaminated with dirt.  Some amount of dirt going through the compressor, combustion, and turbine sections was, I think, an accepted cost of operating on dirt LZ's -- especially if the performance margins were sufficiently tight that you needed reverse thrust in order to make performance numbers work out.
It sounds like the situation in the OP's aircraft is significantly different that what we had, so I suspect that there may be some aircraft-specific concerns at work there.  Or maybe issues of noise (reverse thrust tends to be significantly louder than normal idle) or sucking up FOD into the props (not a concern with our props well above the ground in the Herk).

In addition to FOD, the use of reverse thrust, as pretty much any mechanical system in aircraft  is limited to safest possible minimum.
Using reverse on high power settings imposes considerable loads on structures, and even low power use slowly but certainly wears down the propeller blade adjustment system. These considerations are not a major safety issue as such, but within larger fleets and accumulation of thousands of hours will lead to unnecessary costs. Wheel brakes are the preferred wear item as they are relatively cheap to service and replace.
Flying is and it's procedures are, after all, not only about safety, but very much about economics also.

The guys flying cargo in and out of our local airport in Cessna Caravans also claim that the time spent in reverse thrust has to be accounted for in the plane's log, and is counted against the engine's TBO in a special way. For this reason, they generally avoid using reverse thrust as an airbrake during steep descents- but they claim that just setting the power lever to nearly zero so the prop is turning but generating no thrust is itself an effective speed brake.

Interesting.  In which way(s) is the accounting special or challenging to record?

@RockPaperLz-MaskitorCasket I don't think there's anything _challenging_here; the time in reverse thrust is simply recorded separately from the time in forward thrust because an hour in reverse thrust brings the time before overhaul closer than an hour in forward thrust.

@cjs Thanks. That's what I was thinking too.

As Bianfable stated, FOD ingestion is a big risk when using reverse power settings.  It does come down to an analysis of the runway one is operating on, and a risk assessment of the conditions. Typically on unpaved runways or ones covered in snow or ice, reverse will be discontinued below 40 kias to minimize FOD ingestion risks.  Paved and well cared for runways may allow for max reverse at zero airspeed.


text:
Why is a reciprocating engine air intake a reverse bell shape?
Why would this inlet for the induction system get wider as the air approaches the filter?
What net effect does this have on intake pressure, and how would an inlet that starts wide and then narrows down perform differently?

Related, perhaps a dupe?

Not perhaps, it is a dupe.

Not a jet; indeed maybe a dupe. I'll let the process work itself out if so.

I'm not seeing how this question duplicates the other one, but yes, let the process play out.

It's simply a NACA duct inlet.  On a fully parallel to flow flush surface it has some (but not all) of the effectiveness of a protruding scoop, without the drag.  The curved sides of the ramp act like vortex generators, with the rotation of the vortices on each side pulling air down into the ramp.
On a very clean airplane like one of the RV series homebuilts, that kind of duct can have a measurable benefit.  On a plane like the one pictured, there is a theoretical benefit drag wise, but it would make little detectable difference in that sort of a light plane (with its unfaired nose gear) and is mostly for looks.
In fact since the surface isn't really parallel to the airflow but curves in, the opening is presented more or less directly into the airstream for ram effect and there really isn't a need to create vortices to pull air down the ramp.  A straight sided ramp would work just as well in that particular instance.  Looks cool though, which I suspect is the main reason it's being used there.

The typical shape as pointed out in the question, a diverging nozzle, is for "pressure recovery". For engine efficiency or combustion efficiency, higher static pressure is required. The shape is selected to convert the dynamic pressure (pressure due to velocity) to static pressure, which improves the engine performance.
The opposite shape would be a converging nozzle, that would increase the velocity and decrease the static pressure, which is not what is required for combustion.
What do you see in the image is a typical NACA duct. It recovers pressure at the same time creates a minimum increase in drag (or less total pressure loss). A well designed NACA duct (just the shape is not enough, the air simply won't enter the duct then) ensures a good amount of air intake into the engine.


text:
What is the purpose of the shuttle valve in a Piper Arrow's landing gear system?
This is the PA-28R-201 landing gear hydraulic system diagram.
I am wondering how this shuttle valve functions.  Research I have done indicates that a shuttle valve blocks one attachment to the valve while allowing another to run through.  Only one side or the other, not both or neither.
In the diagram below, everything beneath the shuttle valve is a closed system (other than the thermal relief).
Clearly, the valve cannot be closed on one side or the other or else the pump would be applying pressure through three pistons to a closed valve at the other end of the loop.
Is this shuttle valve different than what I have read them to be?  Is it perhaps in actuality that both sides are either open at the same time or both are closed at the same time but never one closed while one is open? If one remains closed, how could the pump move fluid through the complete circuit?

Can anyone find a better diagram of a shuttle valve that is representative of this particular one?  I think it's really bad.  I know there are several types of shuttle valves, so there is not some catch-all, but looking at this diagram, and not having a mechanical background, I wouldn't know which type to even expect this to be.  From where I'm sitting it almost looks like both sides would always be blocked off...

After doing more research, I think the premise of this question is based on and generated by a bad schematic.  Based on the service manual, the schematic shown in the second answer below is the same system.  In that schematic, it is clear what it is doing.

Your main problem is that the schematic is a completely useless representation.  All the shuttle valve does is connect the extension manifold to the reservoir, when the system isn't pressurized by a selection, to allow the extension side of the actuators to pull fluid directly from the reservoir instead of from the retraction side when the gear is free falling during emergency extension.
It's necessary because there is more actuator fluid volume on the extension side of the actuator than the retraction side, because there is no piston rod taking up space on the extension side.  This means you can't just connect the extend and retract manifolds directly together in a closed loop to let the gear free fall.
When the system is pressurized by either an extend or retract selection (which controls pump motor direction), the shuttle valve blocks the direct connection between the extension manifold and the reservoir, and incorporates the extend manifold into the pressure/return loop so fluid can run to or from the pump from both ends of the actuators.
In the diagram below, the box and line in GREEN is the valve position and fluid path with the system unpressurized.  The box and line in RED is the fluid path and valve position when the system pressurized by an UP or DOWN selection (the reversible pump running).  That's all the shuttle valve does: no selection, extend side of actuators directly routed to reservoir; UP or DN selection, extend side of actuators incorporated into the pressurized hydraulic circuit

The OP's schematic is essentially identical to yours...

The part circled in red?  Are you serious?

This one looks even more confusion overall, but I think I see a piston that would push the check valve open.  So one direction, the check valve opens by virtue of the oil pressure, and on in the other direction a piston pushes it open from the low-pressure side.

The piston (the box) with the spring is the valve.  Whenever the pump is running in either direction, system pressure pushes it to the left against the spring, connecting the pressurized system to the extend manifold directly under it.  When the system not pressurized, the spring pushes the valve to the right and connects the extend manifold directly to the reservoir. I've added stuff to the diagram.

@JohnK that last comment was actually referring to the "Gear up check valve".  At first, I thought, "why is there a check valve it it opens for both directions of flow anyway?"  Then I realized there is a second shuttle or piston-like object that forces that check-vale open, but probably at a higher pressure do to the opposition of the spring and pressure on the check valve from the right side of the diagram.

@JohnK Now, about the shuttle valve, the one in the diagram you've supplied is clear as day as to what it does and why.  The one posted in my question, however, still perplexes me as to its actual operation and neither answer posted has really made it clear.  Could just be a really bad diagram that was never intended to be technically accurate?

Yes, diagrams in pilot handbooks tend to be crude because it's not expected that the pilot needs to know that detail.  The page I posted is from an on-line pdf of the maintenance manual I found after a minute of searching.  If you are learning a type and want to go nuts with the technical aspects of the systems, go to the maintenance manual descriptions.  But remember that you will know way more than most other pilots would care about.

The OP's diagram is sufficient to explain what the shuttle valve does. These types of diagrams do not require every last detail to explain themselves.

The shuttle valve is actuated by high or low pressure depending on what you select, gear up or down. It routes the hydraulic fluid to the bottom of the cylinders to raise the landing gear with high pressure, or to the top of the cylinder to lower them with low pressure and to allow the fluid to return to the reservoir.


text:
Why does only one hydraulic intake line from the reservoir have a filter on the Arrow II?
This is a portion of an Arrow II landing gear hydraulic system diagram.
I noticed that there are two intake check valves, one located on each side of the pump, that would allow flow from the reservoir.  Only one side indicates the existence of a filter.
Why do both sides not have a filter if they are both from the reservoir?

Not sure why the pump's gear up suction has no filter, but see what you can figure out from the horse's mouth: http://www.mikeg.net/library/files/pa28-service.pdf     Hydraulics starts at P297 of the PDF.  Even the diagram and description in the Maint Manual kinda sucks.

@JohnK good deal! Thank you.

It's probably a safety thing, you don't want a blocked filter preventing gear extension.

Why is it designed like that?
This design combines two advantages:

The system works reliably with one filter instead of two, saving a bit of cost, weight, and complexity
In case of a blocked filter, the gears can still be lowered (thanks @GgD for the hint!).

How it works
Gear down:

When the flight deck gear selection handle is put in the gear-down
  position, a switch is made that turns on the electric motor in the
  power pack. The motor turns in the direction to rotate the hydraulic
  gear pump so that it pumps fluid to the gear-down side of the
  actuating cylinders. Pump pressure moves the spring-loaded shuttle
  valve to the left to allow fluid to reach all three actuators.
  Restrictors are used in the nose wheel actuator inlet and outlet ports
  to slow down the motion of this lighter gear. While hydraulic fluid is
  pumped to extend the gear, fluid from the upside of the actuators
  returns to the reservoir through the gear-up check valve. When the
  gear reach the down and locked position, pressure builds in the
  gear-down line from the pump and the low-pressure control valve
  unseats to return the fluid to the reservoir. Electric limit switches
  turn off the pump when all three gears are down and locked.

Gear up:

To raise the gear, the flight deck gear handle is moved to the gear-up
  position. This sends current to the electric motor, which drives the
  hydraulic gear pump in the opposite direction causing fluid to be
  pumped to the gear-up side of the actuators. In this direction, pump
  inlet fluid flows through the filter. Fluid from the pump flows
  thought the gear-up check valve to the gear-up sides of the actuating
  cylinders. As the cylinders begin to move, the pistons release the
  mechanical down locks that hold the gear rigid for ground operations.
  Fluid from the gear-down side of the actuators returns to the
  reservoir through the shuttle valve. When the three gears are fully
  retracted, pressure builds in the system, and a pressure switch is
  opened that cuts power to the electric pump motor. The gear are held
  in the retracted position with hydraulic pressure. If pressure
  declines, the pressure switch closes to run the pump and raise the
  pressure until the pressure switch opens again.

Source: FAA

Aircraft Handbooks & Manuals: FAA-H-8083-31A, Aviation Maintenance Technician Handbook-Airframe Volume 2

chapter 13: Aircraft Landing Gear Systems, pages 13-18 to 13-20

Hydraulic fluid reservoir
Ideally, a hydraulic system could be a closed circuit without a reservoir. The actuators have two cavities, one to push the piston out, and one two pull the piston in. The total volume is constant, except for the volume of the piston rods.
A practical hydraulic system has to cope with the fluid displacement of the piston rods, leakage, geometric imperfections, and the thermal expansion of both, the equipment and the hydraulic fluid. A reservoir of hydraulic fluid is needed to allow fluid to enter or leave the system. This compensation flow could be very minimal. The fluid also needs to get filtered, because of possible impurities in new oil as well as possible contamination from the hydraulic equipment and conducts.
Shuttle valve
The shuttle valve is switching the routing of hydraulic fluid:

When the gears are pulled up, the return flow from the actuators goes to the reservoir, and fluid from the reservoir goes through the filter and the right valve to the pump.
When the gears are pushed down, the system is mostly a closed circuit. There might be some influx of fluid from the right valve, but that would be a small amount (unless the system is leaking badly).

Without the shuttle valve, there would be no point in the circuit where the main stream of fluid goes only one way. In such a design, there would be no place to put a filter out the contamination from within the system.

Deleted. Didn't mean to post.

Nice answer, but I disagree with "The actuators have two cavities, one to push the piston out, and one two pull the piston in. The total volume is constant." This does not account for the rod volume.

@pericynthion You are very right, thanks a lot!  But that means that during gear-down, a volume of fluid equal to the rods enters from the reservoir without filter. That is not a small amount any more.

There really is no point in this case to install a second filter on the low pressure/return hydraulic line in this system. The point of the filter is to ensure the components of the system are protected. The incoming high pressure line filter will do that. If there are any contaminants in the system, they will return harmlessly to the reservoir and the filter will prevent them from being put back into the system. Also, as Bogl stated, you don't want anything interfering with the emergency extension system, which works by releasing pressure from the system. In that case, the hydraulic fluid returns to the reservoir. Anything blocking it on the return path would prevent that extension. Not good.


text:
Learn in-depth about airplane operations
Currently seeking a book or manual that teaches a civilian how a cargo aircraft operates and what it's pilots do, say a 787. Preferably a high-level overview at a per flight phase:

Pre-flight: Flight planning, aircraft checkout (airworthiness), maintenance checking, taxing, ATC communication, etc
Take-off: What do pilots look at during take-off: engine parameters (torque?), airspeed, etc.
Cruise: What do pilots moderate during cruise? What are they doing to prepare for landing?
Landing: Again, what parameters are they looking at, and how often are they looking down? How and what are they communicating to ATC?
Post-flight: What happens to the aircraft? What maintenance is done on the aircraft? What are they doing while they await instructions from ATC? What reports are looked at.

I understand that this is a lot of information to ask for from one book but I am willing to do a lot of reading, from various sources. Any help in answers these questions would be greatly appreciated as well. Young engineer in the aerospace industry and I'd like to learn more.

I'm not aware of any official resources which present all that information in a concise way, but to get a general idea of the operation of a modern civil passenger aircraft you can refer to the manuals provided with flight simulation add-ons. As opposed to the standard aircraft contained in most flight simulators, these payware models are very accurate and highly complex.
Next to the complete manuals, each aircraft typically also contains a tutorial flight manual, where all the steps necessary for the operation are shown in detail (100+ pages each). Here are a few examples:

787: http://qualitywingssim.com/files/ultimate_787_collection/docs/QualityWings%20-%20Ultimate%20787%20Collection%20Tutorial.pdf
A320: https://www.aerosoft2.de/downloads/a318-a319/Aerosoft-Airbus-A318-A319-Vol6-StepbyStep-EN.pdf
Some other Boeing aircraft (PMDG): https://www.precisionmanuals.com/pages/downloads/documentation.html

If you're specifically interested in ATC communications, you can for instance refer to the IVAO documentation about IFR phraseology: https://www.ivao.aero/training/documentation/books/DOC_IFR_phraseology.pdf
Remember that these are NOT official documents, so they are not suitable for any real world use. But in my opinion they are the easiest way to get an idea of aircraft operations. At least that's how I learned it! It has helped me a lot in my Aerospace Engineering studies.


text:
When does the ATC assign runways to aircraft arriving at an airport?
I want to know how far from the airport runways are assigned. Approximately how many nautical miles away or typically how many minutes before landing would the pilot know which runway they'd be landing on? I am specifically interested in large busy airports like DFW, ATL, ORD, etc. Does it vary a lot based on weather and traffic conditions?

At 30-50 miles out, pilots will be listening to the ATIS (or reading it, if Digital ATIS is available), and that will usually list the instrument approach(es) in use. Most importantly, that tells pilots which direction the airport is operating, which might not match the winds since jets can easily operate with a strong crosswind or even a light tailwind. Turning an airport is a giant mess, so they only do it when necessary for safety.
In theory, any flight could be assigned any of the listed approaches. In practice, though, ATC runs major airports so that flights arriving through each arrival gate will usually get the same approach, and ATC will tell pilots to “expect” that approach. For instance, arriving to DFW through the NE or SE gates will usually get you a 17C/35C or 17L/35R approach, and the NW or SW gates a 18L/36R or 13R. (The other runways are mostly used for departures.)
However, if there is a surge of traffic coming in one gate, some flights may be crossed over to balance things out. There is no way to predict that.
Also, nothing stops a pilot from requesting a different approach, and ATC will usually grant it if traffic permits. For instance, a flight that’s running late might try to minimize taxi time by asking for the runway nearest their terminal. They can even request an approach not listed in the ATIS, though that’s much less likely to be granted.
Severe weather can also change things; DFW and a few others are so large that one side may be shut down for storms while the other side pushes planes as fast as possible. Severe weather can also shut down arrival gates, which means the others will see a huge surge in traffic.
The approach isn’t final until ATC clears the flight to execute a particular one, which typically happens 10-20 miles out. It’s a mess for ATC to cancel an approach clearance once issued, and pilots don’t like to switch after they’ve already briefed a certain approach either, which is why there is all that communication ahead of time.

Many many videos on YouTube from Birmingham Airport (BHX) with severe crosswind landings and take-offs.

As a pax, "ATC runs major airports so that flights arriving through each arrival gate" I think of an arrival gate as "B17" or "C23". I presume that's not what you mean here. Can you expand on that a little bit?

@FreeMan That’s a long enough answer that it probably deserves its own question.

Fair enough. Maybe I'll ask.

wow... talk about pressure! ;)

While exact distances & times vary depending on which airport and what runway configuration you're working with, the most reliable answer to the question is, usually on initial contact with the Approach controller.
As an example, here is the SITTH2 RNAV arrival into Atlanta (pdf link):

Inbound to ATL, you'll be cleared for that arrival, and you'll know that regardless of the runway assignment, you can plan to cross SITTH at or above 14,000' and TIZZY at 12,000'.  But as far as runway assignment, you're making a best guess.  Coming in from the southeast like this, the farthest south runway in ATL, runway 10, would be a fair guess, or the outboard of the 9/27 runways (so, 9R -- since they tend to arrive on the outboards, 9R/27L and 8L/26R, and depart on the inboards) if traffic is light. (Airport Diagram for ATL)  But that's not certain until you're talked to Atlanta Approach.
The approach control is the facility that builds the plan to distribute the inbound aircraft (which they can see hundreds of miles out, along with projections when each one will arrive at the "cornerpost" like TIZZY), and they'll have the plan that Delta 123 will get runway 10, Delta 456 will get 9R, American 789 will get 10, and Spirit 987 will get 8L.  And so on initial contact with Approach, the crew will be told, typically, to "Descend via the SITTH2, runway 9R".  At this point, the crew can update (if necessary) the runway in the FMC, review the approach for that runway, and check that the points in the FMC match what the chart shows  (i.e. after TIZZY, going to FRYES and following points for 9R or 10, or to GAASS etc for 8L).
It's not impossible, but it's uncommon for Approach to subsequently change the runway after this, although a crew can always ask.  (The exception to this is Denver; they seem to rebuild their plans every few minutes.)  If there isn't a lot of traffic, ATC may be able to accommodate a crew's request.  In ATL, there isn't a big difference getting to the gate from the north or the south complex; at DFW, it can be a significantly longer taxi, so there are more requests there for "request east side if we can" to try to get a runway corresponding to the terminal where they're parking.
Once the aircraft is on with Tower, it can be possible to switch runways; this is very dependent on traffic and happens only in visual conditions.  This would mostly be swapping to an inboard from an outboard runway, rather than from a north-complex to the south-complex (or vice-versa).  Atlanta doesn't do this much; in Phoenix, it's pretty common, since the inboard runway on the south side of the airport (25R / 7L) is closer to the south-side gates & doesn't involve crossing a runway to get there, as compared to the outboard runway (25L / 7R, which is typically assigned for inbounds to PHX from the south).  If Tower doesn't have anybody getting close to the inboard runway for takeoff, they may offer it to somebody on final.  And the crew can ask -- although if there's somebody who's approaching the runway for takeoff, the answer is likely to be "no."

Out of interest, I'm not a pilot, what is the altitude of Atlanta airport ? I ask since FORCC and AATAT and LAYUH are at 8000' and you talk of approaching at 12000'. I'm also wondering where the names come from e.g. KUNFU (is there fighting ?). Are the loops on the chart areas where one would "circle".

@Carel - very good questions, you should ask those in a separate questions

@Carel The (8) near KUNFU is a distance - to TRAPE in this case, not an altitude. Altitudes on those segments are assigned by the controller. The racetrack patterns shown at FORCC and other fixes are indeed published holding patterns, so ATC can assign "hold at FORCC as published" instead of having to specify inbound course, leg length, and turn direction. There are questions & answers here that discuss the origins of waypoints' names.

@PeterM.-standsforMonica Asking "Is everybody (at) KUNFU fighting" didn't feel like a question one should ask. Thanks RalphJ for the info I'll have a scratch around in the search bars for the waypoint names.

@Carel the eastern waypoints are Star Wars references. SITTH=Sith, SKWKR=Skywalker, LAYUH=Leia, LLNDO=Lando, FORCC=Force, NEWHP=New Hope, AATAT=AT-AT, EEWOK=Ewok, HOTHH=Hoth

@Carel Fix altitudes look like the 14000 at SITTH. The bar below the number means “not below”, likely because there is a different procedure crossing in that vicinity with a “not above” restriction.


text:
Why do both east and west isogonic lines tilt toward the west as they go north?
Here is a picture of the 3 degree east isogonic line just north of Tulsa, OK.

Here is a picture of the 4 degree west isogonic line just east of Nashville, TN.

They both trend westward in relation to true north as you follow the lines northward.  Why do they not go in opposite directions if one is to the east and the other to the west?  This also implies that the 0 degree isogonic line is not parallel to true north.
I checked, and sure enough, it also goes west as you follow it to the north.

Why don't the lines tilt in different directions after crossing over from zero degrees?

Because the present position of the magnetic pole pole is such, that in central and eastern US states the isogonic lines are tilted to the West. But in western parts of the U.S., those lines are tilted to the East...

I thought the isogonic line variation was intended to correct the offset from true north?  If they all tilt the same direction then how could they change from east to west without having paralleled true north at some point?

@Ryan Mortensen There are points where the magnetic declination is zero. Those points define the isoline of declination zero, but that line does not necessarily has a zero inclination in respect of the (geographical) North-South line...

Could you elaborate on this in the answer?  That is what I do not understand.  I was always taught, or at least thought I was taught that the declination was needed to correct to the angle from magnetic north to true north.  Is that not so?  That's my point of confusion.  This answer feels to me to be very distal to my question rather than proximate.

@Ryan The isogonic lines do run directly north–south at certain points. (Just pick a line of latitude, and scan east or west along that line until you find a point where the isogonic lines are running north and south.) But the set of all such points is not, itself, an isogonic line, and in particular, it's not the 0° isogonic line.

@TannerSwett I seem to have a fundamental misunderstanding of the purpose of their existence.


text:
If a pilot takes a MEL checkride and later a SES checkride, is the pilot now also qualified for MES/SEL?
*Assuming all checkrides are passed.
If a pilot gets a multi-engine land rating on a primary checkride, and later takes a checkride as single-engine sea, is the pilot now qualified for multi-engine sea and single-engine land?
I suppose an unspoken question would be, does a multi-engine rating automatically allow for single-engine PIC privileges, or is the restriction between single and multi-engine a 2-way street?

Related, very nearly a dupe: Why do multi-engine privileges not propagate down to single engine?

No. You must take the training and pass the practical test for each add-on rating. See 14 CFR 61.63(c).


text:
Is an area of localized reduced visibility considered to be a cloud?
If there an area containing visible moisture in an otherwise clear sky and that area of visible moisture is transparent is it considered a "thin cloud" or simply a "localized area of reduced visibility"?
What about areas of mist and haze with no definite border below an overcast layer that present in the sky as large areas of reduced visibility still above VFR visibility limitations for aircraft within them?

Does this answer your question? How do the FAR's define a cloud?

@Dave it does not because that answer does not address the spectrum of visibility between what would be considered haze and what would be considered a cloud.  If any "aggregate" of moisture particles constituted a cloud, then any time haze was reported, it would be considered IMC, but it isn't, so there's clearly a spectrum.  You did answer what a cloud is.  I am asking what form of visible moisture isn't a cloud if any.

This might be an answer that works: In meteorology, the definition of fog is less than 1000 m visiblity and mist/haze more than 1000 m visibility.  I think you could reasonably infer the same definition to apply to higher cloud as well.  To the extent you are looking for a go/no/go definition, I think that might be all there is.

Your source actually says, "By international agreement (particularly for aviation purposes) fog is the name given to resulting visibility less than 1 km."  There's the answer.  If you look at the answer Dave is referring to that defines a cloud in the AIM, it says the difference between a cloud and fog is that fog is on the ground. So correlating these, then a cloud would also be something resulting in less than 1km of visibility, but simply not on the ground.

The thing is the linked answer only refers to ground level - fog.   You have to infer the same definition for above-surface layers but I couldn't find anything explicit.


text:
Do check rides completed by part 141 schools with self-examining authority count like normal check rides for CFI renewal and gold seal?
Some schools have self-examining authority issued by the FAA.
Do check rides completed in this manner count the same way as a standard check ride for the purpose of CFI renewal and gold seal applications?

I don't have a reference but I am sure the answer would be YES.

It depends on which FSDO you ask.
I know that the Will Rogers FSDO in Oklahoma City says they do not, but the FSDO in Wichita, Kansas says they do and will take actions on applications accordingly.

Would you please define what "self examining authority" does allow a flight school to do so that we can learn from this?

@Michael Hall it would be best to make a new question about that specifically m

Never mind, a quick Google search answered my question.  P.S.  Have you ever entered an Ernest Hemmingway look-alike contest?  I think you would do well...  ;)


text:
Why would there be a NOTAM for an airport rotating beacon being on continuously?
This NOTAM currently exists at Riverside airport:
!RVS 01/014 RVS AD AP ABN ON CONS 2001141700-2001291700

The rotating beacon is on continuously per this NOTAM.  It has nothing to do with the weather.
Why would an airport do this other than in IFR conditions during the daytime?

It turns out, in this particular case, the reason the rotating beacon was left on during the day time and was NOTAMed as such is because it was broken and could not be turned off by the tower.
What has been gathered is that there is no standard reason why an airport would intentionally leave its rotating beacon on during the day in VMC conditions.

The general convention is that the rotating beacon is only on at night or during IMC. The airport or ATC can choose differently. It would not be the norm and probably should be pointed out to pilots approaching the airport. It would also help identify the airport if there is confusion with multiple nearby airports of similar size and structure.

Would you include some supporting evidence please?

@Ryan, if you are looking for a specific regulation that says "if the beacon is left on during day VFR it shall be NOTAMed" I don't think you will find anything.  NOTAMs are by definition for noting things that are out of the ordinary and of interest to pilots.  It wouldn't be possible to capture and regulate every possible type of situation worthy of being communicated via this medium.

P.S.  There are really two questions here, why NOTAM, and why leave the beacon on.  For the latter we can only speculate here, your best bet to get a specific answer would be to contact the airport.

I did not specify that it must be a regulation. It could be anything. Maybe it has to do with breaking in the bulb or stress testing the motor. Not knowing why is the reason to ask.

@RyanMortensen AIM 2-1-10 d. In Class B, Class C, Class D and Class E surface areas, operation of the airport beacon during the hours of daylight often indicates that the ground visibility is less than 3 miles and/or the ceiling is less than 1,000 feet.

@MichaelHall I was responding to Ryan’s request for supporting evidence.

@JScarry that's true, but that's standard procedure and wouldn't trigger a NOTAM.


text:
Does an AME's advertisement on the back of the medical certificate affect the document's validity under the FAA?
I know a guy who has a medical certificate from an AME based in Dallas Fort Worth, and the front side of the paper has a side-by-side printing of the front and reverse of the FAA medical certificate (FAA form 8500-9) and the back side of the physical paper containing the front and reverse on one side has the AME's website, name and phone number with an airplane graphic.
In short, the back of the paper is a doctor's advertisement.  I have heard rumor that a local DPE says this would make the medical certificate invalid.
Does anyone know of a regulation, LOI, etc. that would confirm or deny this stance on the medical's validity.  Apparently, this AME is quite popular, so if this is true, then that would mean that many pilots currently hold an invalid medical certificate.
I personally find this hard to believe.

It's an interesting question...
The AME Guide gives the following "advice":

Medical Certificates – AME Completion
(Updated 07-26-2017)

Date the medical certificate to reflect the date the medical examination
was performed, NOT the date of import, issuance, or transmission.
Limitations must be selected from the list in the Aerospace Medical Certification
System (AMCS). Additional limitations may NOT be typed/written in.
Signatures: Each medical certificate must be fully completed prior to being
signed.

Both the AME and applicant must sign the medical certificate in ink.
The applicant must sign before leaving the AME’s office.

Give only ONE certificate to the airman
Use AMCS generated certificates only.
Transmit the exam electronically to the FAA using AMCS within 14 days.
The following are NOT valid:

Copies of medical Certificates;
Typewriter or handwritten certificates;
Obviously corrected certificates;
Paper 8500-8 certificates (any remaining paper forms should be destroyed
by the AME).

Replacement medical certificates must be issued by the FAA.

(Remember, the guide, like the Pilot Handbook, is a guide, not regulatory)
The AMCS also gives:

Certificates will be printed on standard printer paper as a single-sided document. Both the front and back sides will be printed on a single sheet of paper that can be folded.

But as far as I can tell in the FAR, the back side (inside when folded) does not have to be blank. As long as the medical certificate follows the 8500-9 and is in a "form prescribed by the Administrator", then it is a valid certificate.
Technically, even if it was against the rules, the medical certificate wouldn't be invalid, just the paper evidence of it would be. As long as the data was entered into AMCS, which it is required to be, the certificate can be reprinted in the proper format for showing anybody who asked.

The signature-related requirements might cause some difficulties for reprints.

I doubt if it would invalidate the certificate. Some reasons:

You can look up the validity of your medical certificate on the FAA website.

The AME should be well aware if this was prohibited, since I'm sure any MD wishing to become an AME would have to attend some kind of formal training at which something like this would be mentioned.

Well that I have never received a medical certificate with anything printed on the back, I have received flyers from some AMEs.

I am a Designated Senior AME in the Southern Region.
I have never seen this gimmick before, neither have I
even seen or heard of a discussion of this modification.
I would therefore say it is not a proscribed practice. I
would go on to say that any airman holding a Medical certificate
that I issued already is quite familiar with my office and contact
info. I get lots of referrals by word of mouth and I do not see how
a printed ad stuck in a wallet would help much.
I would also go on to say that DPEs have a very large block of information
but it does not overlap with the AME world. If challenged, point out
that the certificate is original, doubled signed, and unadulterated since printing.  Ask what Regulatory authority mandates a blank back.
Note well: This is not a statement of Official FAA AMCS policy.

Welcome to aviation.SE!


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Why is training regarding the loss of RAIM given so much more emphasis than training regarding the loss of SBAS?
I've noticed a lack of subject matter on the loss of SBAS as compared to RAIM.
In the ACS there is mention of RNP, SBAS (WAAS), and RAIM, which are all related, but the available content for RAIM and WAAS is much heavier on losses of RAIM than losses of WAAS.
This really became apparent to me when I was searching Garmin G1000 documentation to find annunciations regarding the loss of SBAS, and I noticed that there essentially isn't one other than "APR DWNGRADE" which loosely translates in the manual to, "you lost WAAS capability".
However, the loss of RAIM has a much more clear and direct annunciation, "RAIM UNAVAIL": that needs no translation and is immediately clear that you've lost RAIM.
Why would Garmin not have an "SBAS UNAVAIL" or "WAAS UNAVAIL" annunciation in the same manner as they do for RAIM?  It's almost as if the industry as a whole largely discounts the possibility of SBAS failures.

Here's a list of G1000 NAVIII Annunciations
Here is where WAAS is mentioned in the annunciation list.  Note that the column on the left is the annunciation displayed on the flight deck, but the column on the right is the manual's referenceable extrapolation:

Notice above that neither of the flight-deck-displayed texts on the left which have extended explanations on the right that include "WAAS" also contain "WAAS" or "SBAS" in their in-flight annunciation messages' texts.

Here is where RAIM is mentioned in the annunciation list:

Notice above that the flight-deck-displayed text does contain "RAIM" (twice) for a RAIM loss.

I included the above information to demonstrate my point, and I essentially have three closely-related questions:
Why is Garmin so indirect about the loss of SBAS in their annunciations?
Why do pilots not also perform SBAS predictions like they do for RAIM?
Why is the loss of RAIM given so much more emphasis in training than the loss of SBAS?

Note that LOI is also a loss of RAIM, but it does not mention RAIM explicitly. RAIM UNAVAIL means that RAIM is still available, but does not offer the level of protection needed for the final approach segment. So much for clear interface design...

Your question doesn't define any of the acronyms it uses.  Fortunately (since this question made it into Hot Network Questions), the answers expand them and give enough context to understand the title question for people that know anything about GPS.  Still, the question body is mostly opaque to anyone curious what this is about.

Acronyms are addressed.
https://aviation.meta.stackexchange.com/questions/343/use-of-acronyms-in-questions-answers

FAQ for acronyms: https://aviation.meta.stackexchange.com/questions/347/aviation-acronyms

From a safety perspective RAIM is more critical than SBAS.
If you are flying using GPS, you always rely on RAIM to keep you safe, sometimes you need SBAS too.
Receiver Autonomous Integrity Monitor is a function within an aviation grade GPS receiver that monitors the integrity of the GPS system. Without RAIM, a malfunction in the GPS system can cause large position errors that go unnoticed. These position errors can lead to nuisances such as controlled flight into terrain that really ruin the day.
SBAS on the other hand is (merely) an augmentation to GPS. It improves the vertical accuracy by a few feet, improves the RAIM function so that it is quicker to detect position errors and can detect smaller position errors. But basically, GPS without SBAS is safely usable for the vast majority of applications.
So, if you loose SBAS, you may not be able to perform certain approaches or use certain routes, but RAIM is still there guarding the system integrity.
But if you loose RAIM, the GPS position shown may be correct, or it may be 5 miles off, or 10 miles, or more; it's anybody's guess. The GPS receiver simply has no way to determine whether the calculated position is correct if RAIM is not available.

Now to your questions:
1) Why is Garmin so indirect about the loss of SBAS in their annunciations?
I can't speak for Garmin as to why they emphasize RAIM more than SBAS in their annunciations.
In case of case of the SBAS loss, the annunciation focuses on the operational effect (Approach Downgrade). In case of the RAIM loss, the annunciation focuses on the cause / technical description (RAIM UNAVAIL and LOI).
My guess is that SBAS was added later to their product line as RAIM, and their interface design philosophy had changed from focusing on the technical cause to focusing on the operational effect. For system commonality reasons they did not update their pre-existing RAIM annunciations when adding SBAS.
2) Why do pilots not also perform SBAS predictions like they do for RAIM?
SBAS depends mainly on the availability of a healthy SBAS satellite. The SBAS satellites are predicted to be healthy, and they cover a fixed area of airspace (they are geostationary satellites). The availability status of SBAS in not dynamic; SBAS is predicted to be available.
RAIM depends mainly on the number of GPS satellites visible from the GPS receiver, and how the GPS satellites are distributed over the sky (from the GPS receiver's viewpoint). This is very dynamic, depends on the  total number of GPS satellites in orbit, their health status, their distribution in orbit, the position of the GPS receiver etc. etc. For RAIM to work, the GPS receiver needs at least GPS 5 satellites to be visible (a few degrees above the horizon) and they need to be nicely distributed over the sky. So for RAIM, the situation is very dynamic, but it is predictable. That is why RAIM prediction is done.
3) Why is the loss of RAIM given so much more emphasis in training than the loss of SBAS?
Because, if not properly handled, the loss of RAIM has a much higher probability of killing you than the loss of SBAS.

The RAIM (Receiver autonomous integrity monitoring) is what allows you to fly using a GPS. If you lose RAIM, by regulations you cannot use the GPS to navigate. So, it should not be a surprise for you to have regulators speak more of RAIM than SBAS.
The RAIM basically monitors the accuracy of the navigation. It requires at least five satellites for operation. What it does is it drops one of the satellites at a time and uses the remaining four to calculate the position of the aircraft. This calculated position is then compared to the dropped satellite's measured distance. If this comparison shows an error the GPS or the flight management system warns the pilot that it can no longer accurately give out the position of the aircraft. The RAIM essentially compares the error to the RNP (Required Navigation performance) value. To give you an example, the typical enroute RNP is 2.0. If the error is greater than 2.0 the pilot is alerted. On approach for instance the RNP 0.30. If the error is more than 0.30, the pilot is again alerted and the aircraft can no longer perform the approach. Long story short, RAIM is essential to ensure an accurate GPS navigation.

How Airbus aircraft show loss of GPS accuracy to pilots (Source: https://safetyfirst.airbus.com/gnss-interference/).
The SBAS (Satellite based augmentation system) on the other hand is not something within the aircraft. The SBAS requires ground stations, which measures errors in the GPS signals and provides corrections. This gives a very accurate navigational performance. However, SBAS is not required for most of the GPS based approaches. There is only one type of approach that requires it and that is LPV approach. In an LPV approach you a have both a lateral and vertical guidance generated by the GPS. And it allows you to do approaches up to a traditional ILS category I minima. Normally, you will come across GPS approaches with LNAV and LNAV/ VNAV approaches. In LNAV approaches, only the lateral guidance is given by the GPS, with the vertical guidance expected to be managed by the pilot manually. So, it naturally has a higher minima. In an LNAV/ VNAV approach, still the lateral is managed by the GPS. However, the vertical is now performed by the baro-VNAV. It uses the aircraft altimeter to compute the vertical profile of the approach. This allows LNAV/ VNAV minima to be lower than LNAV only minima. These types of approaches do not require an SBAS. But it requires RAIM. And one last thing. WAAS is purely a US based system and most countries do not receive WAAS signal. There are SBAS stations from many other countries but they are not as good or as widely available as WAAS. So, outside of the States you will rarely find LPV approaches. So, SBAS is not really something of a concern for most airline operators and pilots.
To summarise, SBAS is only required if you want to perform LPV approaches. In all other GPS approaches and other GPS navigation you do not need to have a signal from SBAS. In contrast, RAIM is something within the aircraft systems and it monitors the integrity of the GPS signals. It is important because without such a monitoring system you cannot guarantee your position on the earth. And knowing your position is necessary if you are a pilot flying an aircraft.
I will also answer your questions one by one:
1. Why is Garmin so indirect about the loss of SBAS in their annunciations?
I think Garmin is very direct. It says approach APR DWNGRADE for loss of WAAS. And that is the consequence of losing WAAS. You can no longer perform LPV approaches. Hence, there is an approach downgrade. And if your aircraft does not have an approved baro-VNAV, your minima is that of LNAV only minima. Loss of SBAS has no other real negative affect on your GPS navigational performance.
2. Why do pilots not also perform SBAS predictions like they do for RAIM?
RAIM predictions or monitoring is crucial for navigating using GPS. On the contrary, SBAS availability is not as important as RAIM because it is purely necessary for only one type of GPS approach (LPV).
3. Why is the loss of RAIM given so much more emphasis in training than the loss of SBAS?
The same answer as that for the 2nd question.

"There are SBAS stations from many other countries but they are not as good or as widely available as WAAS"? EGNOS (European SBAS) is considered to have slightly better availability and similar accuracy.


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Why do ADS-B outages occur without simultaneous RAIM outages?
If you check the ADS-B prediction tool and the RAIM prediciton tool on SAPT.FAA.GOV you will see far more ADS-B outages.
What causes ADS-B outages to occur at different times than RAIM outages?  Are ADS-B stations shut down for maintenance?  Is it due to the local weather? or something else?
I know ADS-B systems are reliant on the Global Positioning System to determine location to send in the squitter, so I am assuming that a loss of RAIM is one reason for an ADS-B outage, but what else is causing the additional ADS-B outages not simultaneous to RAIM outages?

RAIM (Receiver Autonomous Integrity Monitoring) is a function within an avaition GPS receiver. It uses redundant measurements for a consistency check to determine the intergrity of the position measurement.
Since RAIM requires redundant measurements, it is only available when there are sufficient measurement sources available. In practice, this mainly boils down to the number of functioning GPS satellites that can be seen from the receiver, and the geometry of the satellites positions relative to the receiver.
For normal RAIM prediction, the RNP integrity limit of 1 or 2 NM is used. This means that the RAIM function needs to be able to verify that the GPS receiver will not produce a lateral position error greater than 1 (or 2) NM with a probability exceeding 10-7 per hour.
The  online predition tool simulates the GPS constellation and calculates whether a GPS RAIM system would be able to reach that integrity limit with the (healthy) satellites in view of the receiver at the time of flight.
For ADS-B, the position transmitted needs to have a certain level of quality in terms of accuracy and integrity. The accuracy of ADS-B position (encoded as NACp) need to be 0.05 NM or below, and the integrity (encoded as NIC) needs to be 0.2NM or below.
To determine the integrity of the ADS-B position, the GPS receiver again uses RAIM. To qualify for ADS-B, not only needs RAIM to be available, it thus needs to determine the integrity at 0.2 NM or less, and at the same time an accuracy of 0.05 NM needs to be achievable.
Since the ADS-B Integrity requirements are much more stringent (0.2 NM vs 1 or 2 NM), the prediction of integrity for ADS-B shows more frequent outages.
Note that the prediction tool only provides a prediction. The actual values during flight may be different.

References:

RAIM prediction requirements FAA AC 20-138D section 5-2.3pdf
ADS-B requirements: 14 CFR 91.227 c) 1) i) & iii)


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Are the turbulence reports by pilots via PIREPs used by other nearby aircraft or air traffic controllers to modify operations in any way?
I know the pilots are required to report turbulence experienced in the aircraft via PIREPs. The data for turbulence with lat,long,alt and the severity is available. I am wondering if the PIREPs are somehow used to modify operations? Or do pilots of other aircraft that will fly through the same region in the future just look out for it without any rerouting?
Also, are there any heuristics on how long the turbulence reported is likely to linger?

Yes, pilots will often modify operations in response to turbulence PIREPs:

Turn on fasten seatbelt sign
Ask flight attendants to be seated
Request a higher or lower altitude where there is less turbulence
Reduce speed to turbulence penetration airspeed (aircraft dependent)

Are turbulence PIREPS used by other pilots?
Especially in Class A airspace, pilots and controllers often exchange information on turbulence in the area.  When a pilot reports it to ATC, it becomes a PIREP.  The controller then uses those PIREPs to advise other aircraft.
How long does the turbulence last?
Turbulence associated with the jet stream can stick around for hours, while turbulence associate with a small thunderstorm may disipate within a few minutes.  It depends on what phenomenon it is associated with.  Generally pilots and controllers only look at PIREPS from the last 60 minutes.

Welcome to Av.SE! Very nice 1st answer - please come back often!

Thank you for the answer. Can you say something about for how long the PIREP information is typically considered valid? Is it for like 10-15 minutes?

@distributedconscious You are welcome!  I added some info on how long they are useful.

Some time spent monitoring ARTCC communications will make it clear that aircraft are frequently asking for and receiving ameded clearances altering their altitude and sometimes route in response to PIREPs regarding turbulence.  Listen for the words "ride report", "any smoother up higher?".  Center controllers often broker these PIREPS, whether or not they are published as UA/UUA's


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What kind of tools are available to an ATC handling traffic in the terminal airspace to predict aircraft trajectories?
I know that the ATC has feedback on the current position of the aircraft via Radar and ADS-B data. However, are there any tools to forecast future trajectories. For example, say an aircraft is scheduled to arrive at an airport and will reach within the coverage of the terminal airspace ATC in the next 5-10 minutes. Does any tool help forecast that aircraft's trajectories based on filed flight plans? Does the ATC pay attention to the aircraft only after the pilot has established contact via voice?
Similarly, let's say the ATC assigned some vectors and maybe allocated a runway to an aircraft. Does any tool predict the trajectory the aircraft would follow so that any future vectoring or allocations can be planned?
If such tools are not available, what is the ATC process for handling terminal airspace traffic?

Typically radar displays include a target and a projected course (which is just a minute or two long I think), are you asking about something much further into the future?

Yes, there are several ways for the controller to predict the trajectory of a flight. The closer the flight gets, the more precise the predictions also get.
It all begins with a flightplan. Prior to departure, a flightplan will have been sent to all ATC units expected to be involved with handling the flight. This includes an estimated time of departure (EOBT) and an estimated elapsed time (EET). Based on these, you can roughly predict when a flight will enter your airspace. The estimated time of departure in a flightplan, however, is not very accurate, since the flight is allowed to deviate from it with +/- 15 minutes.
In some cases, when the flight takes off, a departure message (DEP) will be sent to everyone who has received the flightplan. The DEP message contains an actual time of departure, which allows you (again based on flightplan data including EET) to calculate a more precise estimated time of entry into your airspace. This is still not very precise, since many different things can happen enroute that means the flight arrives some minutes earlier or later than expected.
Next step is coordination. For IFR flights, every transition from the area of responsibility of one ATC unit to the next requires prior coordination. Controllers often do this manually (via phone), but more and more systems support automatic coordination and exchange of estimates, for example via "On-Line Data Interchange" (OLDI) or other electronic message formats. You will typically receive a coordination for a flight somewhere around 5-10 minutes before it enters your airspace. The coordination will contain a precise estimate of when exactly the flight enters your airspace. The required precision for such an estimate is typically in the range of 3-5 minutes (if a delay occurs after the coordination has happened, exceeding the 3-5 minute tolerance, a new coordination has to be done). This is really the point at which the controller will start "paying attention to the flight" as you say.
Up until now, the flight has still not checked in to your frequency, but that is the next step.
When the flight calls you - assuming a radar based environment - you should be able to identify the flight on the radar. This gives you a precise location for the flight, along with current level, track and ground speed. Knowing these values lets you extrapolate the trajectory of a flight quite accurately. System complexity varies, but common for all radar systems I know is the option to show a "prediction vector". This is a vector (straight line) drawn from the radar track symbol of a flight in the direction of travel for a certain length, commonly based on the ground speed. For example, in a terminal environment, you might have 2-minutes prediction vectors enabled for all tracks, which means that, for all radar tracks, the system will draw a line indicating where the aircraft will travel in the next two minutes (assuming, and this is important, constant heading and ground speed). This is a very intuitive way to visualise for the controller both the current heading of a flight, and its speed, which is useful in many different situations. The controller usually has the option to change the look-ahead time of the prediction vector, either for all tracks or for a single flight, typically in 1-minute intervals.

The green lines shown here are prediction vectors
Note that a prediction vector only works based on current heading and ground speed. A change of either of these will change the prediction vector. There are systems that take into account the planned route of a flight when predicting the trajectory, such as Medium Term Conflict Detection (MTCD), but these are mainly used in the enroute (ACC) environment. In the terminal environment, aircraft are climbing and descending, which means they are constantly changing (ground) speed. Also, many aircraft in the terminal environment are under radar vectors, which means they are not following predefined routes, so the system has no way of knowing if and when an aircraft is going to make a turn (since this is decided by the air traffic controller on short notice). These factors make tools such as MTCD pretty much useless in the terminal environment.
There are also trajectory based safety nets, although that's not exactly what you are asking.
Short Term Conflict Alert (STCA) is used to warn the controller of possible impending losses of separation between two radar tracks. You can think of STCA as working similar to a prediction vector, the main difference being that the STCA uses a 3-dimensional vector, since vertical movement is considered as well as horisontal movement. However, just like a prediction vector, STCA only considers what the aircraft is doing right now and extrapolates that into the future. The system does not know if a flight is going to make a turn or level off in 10 seconds. Because of this, the threshold values for triggering an STCA are usually set lower that actual separation minima, to reduce the number of nuisance alerts (e.g. if the required separation is 1000 ft, an STCA might be set to trigger if the predicted separation is less than 800 ft).
There are also tools such as Minimum Safe Altitude Warning (MSAW) and Area Proximity Warning (APW/AIW) which present a warning to the controller if a flight is descending lower than a defined safe altitude or about to enter some sort of restricted airspace. For the most part though, these are based on current position and altitude of a flight, not predicted trajectory.
As for the last part of your question, no, there are no tools that tell the controller how to vector a flight. After all, that is what we are trained for and do very well. With commonly available computing power, there are simply too many variables to consider for a computer to vector and sequence aircraft as efficiently as a human controller. Although, in my opinion, it is probably just a matter of time before supercomputers can more or less take over such tasks.

What a great answer!  Could you clarify or add an example for this sentence? Because of this, the threshold values for triggering an STCA are usually set lower that actual separation minima, to reduce the number of nuisance alerts. If actual separation mins are 10 miles (making up values) would you set STCA thresholds to 9 or to 11?

In that image, are DLH2VY and GOGSK on the same prediction vector?

@SteveV. Added clarification. 9 would be the answer in your example

@Bergi The prediction vectors for those two flights appear to be overlapping, so it looks as one line

Nice answer, however there are indeed Vector-to-Final assistant systems! They will tell the controller exactly when to turn an aircraft on downwind to Final to receive the exact separation for maximum efficiency - based on WTC, speed and level of all aircraft involved

@pcfreakxx That's really interesting. I know of AMAN which, combined with point-merge, probably gets quite close to automated sequencing and spacing, but I've never heard of a system like the one you describe. Do you have any source for further reading?

@expeditedescent No unfortunately not. But I believe it’s called „spacing assistant“

Hmm if that's the case, I wouldn't exactly call that a tool for automatic vectoring - it's simply a way to visualise to the controller the required separation between two tracks in an environment where there are many different separation minima based on the actual pair of aircraft and current wind

@expeditedescent That’s not what I was referring to

@SteveV. it would be 9.

iFACTS is a product that has been in use for almost 10 years in UK ATC. It will predict 18 minutes ahead (in UK airspace as this is the longest time a flight would require to get through the longest sector. This is configurable) for every flight of interest and do conflict detection for all flights of interest (with appropriate filtering rules depending on MOPS). The predictions are based on the physical aircraft performance model, long/short haul characteristics, wind direction and obvioiusly the flight plan including any tactical clearances (e.g. when an aircraft is asked to change altitude due to a change in air traffic during a flight), coordinations (when you enter/leave a sector) and a few other things..
The conflict detection also includes aircraft that haven't yet taken off or have lost radar contact.
iFACTS is unique in the world as a tools support system for air traffic controllers, but is set to be delivered into other countries as part of the Single European Skies initiative.
Edit (I realised I hadn't answered the rest of your question) Terminal control and national ATC are different. Controlled airspace is considered to be everything above 4000ft. Each terminal at the moment (although this will change) has their own air traffic controllers who communicate to the aircraft to bring them in/out along with ground movements and all those comms also go to national ATC.  Terminal control doesn't have iFACTS (this will change) due to the software changes required.

what exactly is unique in the world about iFACTS? From what you described it appears that German ATC systems use the same system - only difference is that it predicts 20 minutes ahead instead of 18.

It sounds to me like a form of MTCD - or is it something else?

It does do MTCD as well as flight path monitoring, alerts for non-conformance, coordination handling etc. @pcfreakxx can you reference? I'm interested -- what's its product name?

@DavidBoshton iCas, developed by INDRA. It does the exact same as you describe + more

Interesting. Indra don't have the capability and ICas is not listed as an MTCD system nor does it have flight path monitoring (according to their press release and feature page). In fact there is a project which integrates iFACTS with iTEC, Indra's offering, and uses the modelling and predictive capabilities of iFACTS as a service add on to iTEC.

@DavidBoshton Interesting - then their feature page might be pretty old. We‘ve been working with this system (including MTCD, FPM, EDFL, 4D trajectories, automatic coordination, what-if-probes and so on) for more than 10 years now...


text:
What is the function of this small hole on the B737's hydraulic reservoir line?
This is picture of a B737-800. When you open the bleed system a small amount of air is discharged from this hole (marked with an arrow, lower right). What is it for? And what happens if this hole gets clogged?
AMM Part I Reference 29-09-00, page 3.

Click images for higher-res.

Do you have a closeup of that??

@Federico at the end of the pipe the red arrow points to I think.

@Notts90 thanks. in my brain it was only a red pipe.

Red arrow shows to small hole. Small hole is end of the pipe plug.

Amm part 1 referance 29-09-00 page 3.

Answering based on ATA 49 system, B757/767 APU Surge Control Valve muscle air plumbing.
Some pneumatic sensing and pressure systems have a moisture bleed hole to prevent icing in the system.  They are typically located at a low point or bend in the line to allow water to escape the system while maintaining pressure.  If the hole gets plugged it can prevent moisture from escaping and ice to form in the line.


text:
How does an RMI respond when tuned to a VOT station?
I know that a VOT station for testing VORs broadcasts a 360 radial signal, so on a VOR, the indication would be 360 with a 'FROM' or 180 with a 'TO' indication, but how does an RMI respond if tuned to a VOT station?
Would the RMI simply home to the station because it points to the direction signal is coming from, or would it point at the 180 position because it detects that it is on a 360 radial 'FROM' the station?

Yes, it will point at the 180 position
VOR Test

A VOT differs from a VOR in that it replaces the variable directional signal with another omnidirectional signal, in a sense transmitting a 360° radial in all direction

VOR Receiver Check

With the Course Deviation Indicator (CDI) centered, the omni−bear- ing selector should read 0 degrees with the to/from indication showing “from” or the omni−bearing selector should read 180 degrees with the to/from indication showing “to.” Should the VOR receiver operate an RMI (Radio Magnetic Indicator), it will indicate 180 degrees on any omni−bearing selector (OBS) setting.

RMIs don't have an OBS knob though, right?  I thought with a VOR, they would normally just always point to the station in the same manner as an ADF points to an NDB without a manual selection (other than the frequency).  So another way of asking my question is, is the principle of operation of an RMI signal strength modulation(like ADF/NDB) or utilization of the phase difference sent by the VOR.

@ymb1 I just re-read that -- "Driven by a VOR receiver".  So a VOR unit passes information to an RMI, and the RMI does not have its own computation equipment?